1. Field of the Invention
The present invention relates to an inwheel motor system for use in a vehicle having direct drive wheels as drive wheels and to an inwheel motor mounting method.
2. Description of the Prior Art
Nowadays, an inwheel motor system that a motor is incorporated in each wheel is been adopted in vehicles which are driven by a motor, such as electric cars, to achieve a high space efficiency and high transmission efficiency of driving force.
FIG. 78 shows that a direct drive motor of a hollow outer rotor type (inwheel motor) 70 disclosed by JP 2676025 is mounted. In this inwheel motor 70, a stator 70S is connected to and supported by an upright 71 which is a fixed portion, located on the inner side of the wheel disk 73 of a direct drive wheel 72, and also connected to a rotary shaft 74 coupled to the above wheel disk 73 through a bearing 74J. A rotor 70R around the above stator 70S is supported by a first bracket 75a connected to the above rotary shaft 74 and a second bracket 75b which is rotatably fixed to the upright 71 through a bearing 71J. Since the rotor 70R is thereby rotatably connected to the stator 70S, torque can be transmitted to the wheel 72 by driving the inwheel motor 70 so that the wheel 72 can be directly driven.
There are proposed some methods of mounting an inwheel motor: one shown in FIG. 79 in which a rotor 80R having magnetic means (permanent magnet) 80M is installed in a housing 82 fixed to a wheel 81, a stator 80S having a coil 80C is placed on the inner side of the above magnetic means 80M and fixed to a hollow shaft 84 connected to a knuckle 83, and the inner and outer side walls 82a and 82b of the above housing 82 are connected to the above stator 80S through bearings 84a and 84b to rotatably link the rotor 80R of an inwheel motor 80 to the stator 80S (for example, Japanese Patent Publication No. 9-506236), and one shown in FIG. 80 in which the stator 90S of an inwheel motor 90 is fixed to a steering knuckle 93 connected to a hub portion 92 through a bearing 91 and in which the rim portion 94a of a wheel 94 is used as the rotor of the motor to be rotatably linked to the stator 90S (for example, Japanese Laid-open Patent Application No. 10-305735).
In a vehicle having a suspension unit such as a spring around each wheel, as the mass of an unsprung part such as a wheel, knuckle or suspension arm, so-called “unsprung mass” increases, the contact force of a tire fluctuates when the vehicle runs over a uneven road, resulting in deteriorated road holding properties.
Even when the mass of the body of a vehicle, so-called “sprung mass” is small, the road holding properties also deteriorate. Therefore, to improve the road holding properties, the unsprung mass must be made much smaller than the sprung mass.
However, since the motor stator of the inwheel motor is rotatably fixed to a spindle shaft connected to a part called “upright” or “knuckle” which is one of parts around the wheels of the vehicle, the unsprung mass increases when the above inwheel motor is mounted, thereby deteriorating the road holding properties.
Therefore, the inwheel motor vehicle is rarely used although it is a very attractive electric car having excellent space efficiency and transmission efficiency of driving force.